Add SV_BaseVertexLocation and SV_StartInstanceLocation to VSIn

[tex3d]

These would return the index start offsets passed to DrawIndexedInstanced in the corresponding BaseVertexLocation and StartInstanceLocation arguments. GLSL has the equivalent values: gl_BaseVertex and gl_BaseInstance. While the names are long, they match the API, and consistency is important.

These have been an ongoing request, and can save extra root argument overhead required to get these without built-in support.

edited to fix BaseVertexLocation name (StartVertexLocation is from DrawInstanced, not DrawIndexedInstanced).

[AdamJMiles]

While we do have StartInstanceLocation in the API, the other one I think corresponds to BaseVertexLocation? There's no 'StartVertexLocation' in the Draw command API.

[sebbbi]

DrawIndexedInstanced arguments and the indirect argument struct has these:

  UINT IndexCountPerInstance,
  UINT InstanceCount,
  UINT StartIndexLocation,
  INT  BaseVertexLocation,
  UINT StartInstanceLocation

gl_BaseInstance = StartInstanceLocation
gl_BaseVertex = BaseVertexLocation

[otanter-at-ubi]

I second all of these. We've asked for them a few years ago at the xfest.

[lijianwen13]

I think it's very important for us to build cross-platform game engines.

[yuriy-odonnell-epic]

+1e9 to this. Implementing advanced cross-platform GPU-driven rendering techniques is extremely inconvenient without automatic SV_StartInstanceLocation. Workarounds exist, but they're very yucky.

[kingofthebongo2008]

something about this?
if someone wants to help, where one can look?